Kongming lock(孔明锁Kǒngmíngsuǒ) is a traditional Chinese intellectual toy. It is said that the toy was invented by Zhuge Kongming(诸葛孔明Zhūgé Kǒngmíng) some 2,000 years ago based on the principles of the eight-diagram metaphysics(八卦玄学). It was widely popular among the folks. The concave and convex parts inside the three-dimensional interpolation toy mesh perfectly. Kongming locks come in different shapes and sizes, with different internal structures. But they are usually easy to take apart and difficult to reassemble.
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